A photo of your watch with current activity is good as a proof of running until Garmin outage is done.

Max photo size: 4MB

The following could be considered as proofs of activity: Garmin Connect / Strava / Movescount / Fitbit / Runkeeper / Endomondo, Nike+ or Adidas app screenshots or even photos of your running watches. Whatever apps you are using to record your activity, make sure the date and distance are clearly visible in the screenshots provided.